There have conventionally been developed various types of backlight units that supply light to a liquid crystal display panel (a non-light-emitting display panel) for a liquid crystal display device. Among light sources included in an area light-type backlight unit and the like is a fluorescent tube such as a hot cathode tube or a cold cathode tube.
In a case in which such fluorescent tubes are used, the brightness is high in portions over the fluorescent tubes, but in contrast, the brightness is low in portions over gaps between adjacent ones of the fluorescent tubes. This leads to a comparatively significant difference in brightness (light amount nonuniformity) between portions over the fluorescent tubes and portions over gaps between adjacent ones of the fluorescent tubes. Such light amount nonuniformity is called a lamp image, which is one of factors that degrade the quality of light (backlight light) from a backlight unit.
There have been invented various types of backlight units for eliminating the lamp image (see, for example, Patent Document 1). Among the simplest ones of such backlight units is a backlight unit 149 as shown in the sectional view of FIG. 10. In the backlight unit 149, reflection areas ‘ar’ are formed in a light receiving surface 146R of a diffusion sheet 146 located the closest to fluorescent tubes 142.
Most part of light traveling upward (directly upward) from the fluorescent tubes 142 is reflected by the reflection areas ‘ar’, and does not directly enter the diffusion sheet 146. This prevents the portions over the fluorescent tubes 142 from becoming excessively bright, leading to elimination of the lamp image.
Patent Document 1: JP-A-2003-279979